In filling machines, it is known to control how much filling material enters a container. This involves the use of a probe that extends into the container being filled. Among the known probes are electrical filling-level probes with a probe contact, and return gas pipes.
When immersed in the rising level of the filling material during filling of the container, the electrical filling-level probe delivers a probe signal that causes a liquid valve to close such that the respective target filling level in the container is attained.
A disadvantage of the electrical filling-level probe arises from the possibility that the probe contact and/or of electronics processing the probe signal may fail. When this occurs, the container may be over-filled.
Another known probe for determining the filling height is a return gas pipe. During the filling of a container arranged in a sealed position against the filling element, the return gas pipe conducts away any return gas displaced from the interior. The rising liquid level in the container eventually immerses the return gas pipe. Immersion of the gas pipe interrupts the flow of return gas through it, thus terminating any further inflow of the filling material into the container after the target filling level has been reached. As a result, positioning the return gas pipe along the axis amounts to controlling the filling level.
An advantage of using a return gas pipe as a probe is that one no longer has to worry about a fault with a probe contact and/or a fault in the electronics that processes the probe signal.
A disadvantage of filling systems with return gas pipes is that the liquid valve that supplies the filling material may not be closed immediately. In most cases, it is only closed after some time, for example when a filling station has reached a predetermined angle on a rotating transport element. As a result the liquid valve is closed only after the target filling height has long since been reached. During this time interval, there may be faults, such as pressure fluctuations, sudden changes in the circulation speed of the transport element, and/or vibrations. As a result of these faults, the container may become overfilled.
Another disadvantage is that sometimes, even after the return gas pipe has been immersed, filling material will still rise far into the return gas pipe or into its gas channel. As a result, after filling, it becomes necessary to empty the return gas pipe into the container to avoid having filling material drip after removing the filled container from the filling element. The time required for the emptying of the return gas pipe reduces performance, or throughput, of the filling machine. There is also the risk that contaminated filling material from a contaminated container will find its way into subsequent containers.